Various theories have been formulated in connection with the structure and organization of the intelligence. Out of these three theories are important.

1) Connection Theory (By Thorndile) or Multi-Factor Theory.

2) Two-Factors Theory (By Spearman).

3) Group factor or Primary mantel abilities Theory. (By Thurstone).

1) Connection Theory or Multi-Factor Theory. (By Thorndile):

According to him the basis of intelligence are neural connections between stimulus and response that under lie behavior. According to this theory a person might be able to earn success in abstract learning but not in social relationships or in mechanical activities. Successful achievements in two or three areas would result from overlapping of the intelligence rather than functioning of general intelligence. Intelligence is a multitude of atoms of mental ability. This theory is also called as atomistic theory. The main assumption of this theory is that mental activity involves a number of atoms of mental energy which function together.

2) Two Factory Theory (By Spearman):

He says that ‘intelligent’ behavior is affected by two mental ability factors:

a) General intelligence (G.factor)

b) Specific abilities (S. factors):

The G and S factors are working together in a unit. Generally G factor of intelligence is not found in the same proportion among all individuals. Variations in G factors are due to individual differences. Concept of a G factor is the physical energy of the individuals. G factor is a general energy that functions in all mental activity, but such as mathematics, language, science or any special ability. G factor is gifted ability of the individual.

3)Group Factor or Primary Mental Ability Theory (By Thrustone):

This theory is most popular because it has led to construction of famous chieqge tests and primary mantel abilities. According to him there is a primary factor operation in different mental activities of a common nature. Thus it is assumed that there are number of group of mental abilities having their own primary factors is to provide unity and cohesion to group of mental activities. Thurstone evolved a multiple factor theory including thirteen factors.